Turbine component other than airfoil having ceramic corrosion resistant coating and methods for making same

ABSTRACT

An article comprising a turbine component other than an airfoil having a metal substrate and a ceramic corrosion resistant coating overlaying the metal substrate. This coating has a thickness up to about 5 mils (127 microns) and comprises a ceramic metal oxide selected from the group consisting of zirconia, hafnia and mixtures thereof. This coating can be formed by a method comprising the following steps: (a) providing a turbine component other than an airfoil comprising the metal substrate; (b) providing a gel-forming solution comprising a ceramic metal oxide precursor; (c) heating the gel-forming solution to a first preselected temperature for a first preselected time to form a gel; (d) depositing the gel on the metal substrate; and (e) firing the gel at a second preselected temperature above the first preselected temperature to form the ceramic corrosion resistant coating comprising the ceramic metal oxide. This coating can also be formed by alternative methods wherein a ceramic composition comprising the ceramic metal oxide is deposited by physical vapor deposition on the metal substrate to provide a strain-tolerant columnar structure, or is thermal sprayed on the metal substrate.

REFERENCE TO PREVIOUS APPLICATIONS

This application is a Division of co-pending U.S. patent applicationSer. No. 11/094,351 filed Mar. 31, 2005.

BACKGROUND OF THE INVENTION

This invention broadly relates to turbine components other thanairfoils, such as turbine disks, turbine seals and other staticcomponents, having thereon a ceramic corrosion resistant coating. Thisinvention further broadly relates to methods for forming such coatingson the turbine component.

In an aircraft gas turbine engine, air is drawn into the front of theengine, compressed by a shaft-mounted compressor, and mixed with fuel.The mixture is burned, and the hot exhaust gases are passed through aturbine mounted on the same shaft. The flow of combustion gas turns theturbine by impingement against the airfoil section of the turbineblades, which turns the shaft and provides power to the compressor. Thehot exhaust gases flow from the back of the engine, driving it and theaircraft forward. The hotter the combustion and exhaust gases, the moreefficient is the operation of the jet engine. Thus, there is incentiveto raise the combustion gas temperature.

The compressors and turbines of the turbine engine can comprise turbinedisks (sometimes termed “turbine rotors”) or turbine shafts, as well asa number of blades mounted to the turbine disks/shafts and extendingradially outwardly therefrom into the gas flow path. Also included inthe turbine engine are rotating, as well as static, seal elements thatchannel the airflow used for cooling certain components such as turbineblades and vanes. As the maximum operating temperature of the turbineengine increases, the turbine disks/shafts and seal elements aresubjected to higher temperatures. As a result, oxidation and corrosionof the disks/shafts and seal elements have become of greater concern.

Metal salts such as alkaline sulfate, sulfites, chlorides, carbonates,oxides, and other corrodant salt deposits resulting from ingested dirt,fly ash, concrete dust, sand, sea salt, etc., are a major source of thecorrosion, but other elements in the aggressive bleed gas environment(e.g., air extracted from the compressor to cool hotter components inthe engine) can also accelerate the corrosion. Alkaline sulfatecorrosion in the temperature range and atmospheric region of interestresults in pitting of the turbine disk/shaft and seal element substrateat temperatures typically starting around 1200° F. (649° C.). Thispitting corrosion has been shown to occur on critical turbine disk/shaftand seal elements. The oxidation and corrosion damage can lead topremature removal and replacement of the disks/shafts and seal elementsunless the damage is reduced or repaired.

Turbine disks/shafts and seal elements for use at the highest operatingtemperatures are typically made of nickel-base superalloys selected forgood elevated temperature toughness and fatigue resistance. Thesesuperalloys have resistance to oxidation and corrosion damage, but thatresistance is not sufficient to protect them at sustained operatingtemperatures now being reached in gas turbine engines. Disks and otherrotor components made from newer generation alloys can also containlower levels of aluminum and/or chromium, and can therefore be moresusceptible to corrosion attack.

Corrosion resistant diffusion coatings can also be formed from aluminumor chromium, or from the respective oxides (i.e., alumina or chromia).See, for example, commonly assigned U.S. Pat. No. 5,368,888 (Rigney),issued Nov. 29, 1994 (aluminide diffusion coating); and commonlyassigned U.S. Pat. No. 6,283,715 (Nagaraj et al), issued Sep. 4, 2001(chromium diffusion coating). A number of corrosion-resistant coatingshave also been considered for use on turbine disk/shaft and sealelements. See, for example, U.S. Patent Application No. 2004/0013802(Ackerman et al), published Jan. 22, 2004, which discloses metal-organicchemical vapor deposition (MOCVD) of aluminum, silicon, tantalum,titanium or chromium oxide on turbine disks and seal elements to providea protective coating. These prior corrosion resistant coatings can havea number of disadvantages, including: (1) possibly adversely affectingthe fatigue life of the turbine disks/shafts and seal elements becausethese prior coatings diffuse into the underlying metal substrate; (2)coefficient of thermal expansion (CTE) mismatches between the coatingand the underlying metal substrate that can make the coating more proneto spalling; and (3) more complicated and expensive processes (e.g.,chemical vapor deposition) for depositing the corrosion resistantcoating on the metal substrate.

Accordingly, there is still a need for coatings for turbine disks,turbine shafts, turbine seal elements and other non-airfoil turbinecomponents that: (1) provide corrosion resistance, especially at higheror elevated temperatures; (2) without affecting other mechanicalproperties of the underlying metal substrate or potentially causingother undesired effects such as spalling; and (3) can be formed byrelatively uncomplicated and inexpensive methods.

BRIEF DESCRIPTION OF THE INVENTION

An embodiment of this invention broadly relates to an article comprisinga turbine component other than an airfoil having a metal substrate and aceramic corrosion resistant coating overlaying the metal substrate,wherein the ceramic corrosion resistant coating has a thickness up toabout 5 mils (127 microns) and comprises a ceramic metal oxide selectedfrom the group consisting of zirconia, hafnia and mixtures thereof.

Another embodiment of this invention broadly relates to a method forforming this ceramic corrosion resistant coating on the underlying metalsubstrate of the turbine component. One embodiment of this methodcomprises the following steps:

(a) providing a turbine component other than an airfoil comprising ametal substrate;

(b) providing a gel-forming solution comprising a ceramic metal oxideprecursor;

(c) heating the gel-forming solution to a first preselected temperaturefor a first preselected time to form a gel;

(d) depositing the gel on the metal substrate; and

(e) firing the deposited gel at a second preselected temperature abovethe first preselected temperature to form a ceramic corrosion resistantcoating comprising a ceramic metal oxide, wherein the ceramic metaloxide is selected from the group consisting of zirconia, hafnia andmixtures thereof.

An alternative embodiment of this method for forming this coatingcomprises the following steps:

(a) providing a turbine component other than an airfoil comprising ametal substrate; and

(b) depositing a ceramic composition comprising a ceramic metal oxide onthe metal substrate by physical vapor deposition to form a ceramiccorrosion resistant coating comprising the ceramic metal oxide andhaving a strain-tolerant columnar structure, wherein the ceramic metaloxide is selected from the group consisting of zirconia, hafnia andmixtures thereof.

Another alternative embodiment of this method for forming this coatingcomprises the following steps:

(a) providing a turbine component other than an airfoil comprising ametal substrate; and

(b) thermal spraying a ceramIC composition comprising a ceramic metaloxide on the metal substrate to form the ceramic corrosion resistantcoating comprising the ceramic metal oxide, wherein the ceramic metaloxide is selected from the group consisting of zirconia, hafnia andmixtures thereof.

The ceramic corrosion resistant coating of this invention provides anumber of significant benefits and advantages. Because the ceramiccorrosion resistant coating comprises a zirconia and/or hafnia as theceramic metal oxide, it does not diffuse into the underlying metalsubstrate. As a result, the ceramic corrosion resistant coating does notadversely affect the fatigue properties of the coated turbinedisk/shafts, seal elements and other turbine components.

Because of the greater coefficient of thermal expansion match betweenthe ceramic metal oxide and the underlying metal substrate, the ceramiccorrosion resistant coating of this invention provides greater adherenceto the substrate and thus greater resistance to spalling. This increasedadherence will also further improve the fatigue properties of the coatedturbine disks/shafts, seal elements and other turbine components byresisting propagation ofcracks though the thickness of the coating intothe metal substrate.

These ceramic corrosion resistant coating can be formed by embodimentsof the method of this invention that are relatively uncomplicated andinexpensive. In addition, the ceramic corrosion resistant coating can beformed by embodiments of the methods of this invention as a relativelythin layer on the metal substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a portion of the turbine sectionof a gas turbine engine.

FIG. 2 is a sectional view of an embodiment of the ceramic corrosionresistant coating of this invention deposited on the metal substrate ofa turbine rotor component.

FIG. 3 is a frontal view of a turbine disk showing where the ceramiccorrosion resistant coating of this invention is desirably located.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “ceramic metal oxide” refers to zirconia,hafnia or combinations of zirconia and hafnia (i.e., mixtures thereof).These ceramic metal oxides were previously used in thermal barriercoatings that are capable of reducing heat flow to the underlying metalsubstrate of the article, i.e., forming a thermal barrier, and whichhave a melting point that is typically at least about 2600° F. (1426°C.), and more typically in the range of from about from about 3450° toabout 4980° F. (from about 1900° to about 2750° C.). The ceramic metaloxide can comprise 100 mole % zirconia, 100 mole % hafnia, or anypercentage combination of zirconia and hafnia that is desired.Typically, the ceramic metal oxide comprises from about 85 to 100 mole %zirconia and from 0 to about 15 mole % hafnia, more typically from about95 to 100 mole % zirconia and from 0 to about 5 mole % hafnia.

As used herein, the term “ceramic metal oxide precursor” refers to anycomposition, compound, molecule, etc., that is converted into or formsthe ceramic metal oxide, for example, from the respective ceramic metalhydroxide, at any point up to and including the formation of the ceramiccorrosion resistant coating.

As used herein, the term “ceramic corrosion resistant coating” refers tocoatings of this invention that provide resistance against corrosioncaused by various corrodants, including metal (e.g., alkaline) sulfates,sulfites, chlorides, carbonates, oxides, and other corrodant saltdeposits resulting from ingested dirt, fly ash, concrete dust, sand, seasalt, etc.; at temperatures typically of at least about 10000 p (538°C.), more typically at least about 12000 p (649° C.), and which comprisethe ceramic metal oxide. The ceramic corrosion resistant coatings ofthis invention usually comprise at least about 60 mole % ceramic metaloxide, typically from about 60 to about 98 mole % ceramic metal oxide,and more typically from about 94 to about 97 mole % ceramic metal oxide.The ceramic corrosion resistant coatings of this invention furthertypically comprise a stabilizing amount of a stabilizer metal oxide forthe ceramic metal oxide. These stabilizer metal oxides can be selectedfrom the group consisting of yttria, calcia, scandia, magnesia, india,gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia,praseodymia, lanthana, tantala, etc., and mixtures thereof. Theparticular amount of this stabilizer metal oxide that is “stabilizing”will depend on a variety of factors, including the stabilizer metaloxide used, the ceramic metal oxide used, etc. Typically, the stabilizermetal oxide comprises from about 2 about 40 mole %, more typically fromabout 3 to about 6 mole %, of the ceramic corrosion resistant coating.The ceramic corrosion resistant coatings used herein typically compriseyttria as the stabilizer metal oxide. See, for example, Kirk-Othmer'sEncyclopedia of Chemical Technology, 3rd Ed., Vol. 24, pp. 882-883(1984) for a description of suitable yttria-stabilizedzirconia-containing ceramic compositions that can be used in the ceramiccorrosion resistant coatings of this invention.

As used herein, the term “ceramic composition” refers to compositionsused to form the ceramic corrosion resistant coatings of this invention,and which comprise the ceramic metal oxide, optionally but typically thestabilizer metal oxide, etc.

As used herein, the term “turbine component other than an airfoil”refers to those turbine components that are not airfoils (e.g., blades,vanes, etc.) that are formed from metals or metal alloys, and includeturbine disks (also referred to sometimes as “turbine rotors”), turbineshafts, turbine seal elements that are either rotating or static,including forward, interstage and aft turbine seals, turbine bladeretainers, other static turbine components, etc. The turbine componentfor which the ceramic corrosion resistant coatings of this invention areparticularly advantageous are those that experience a service operatingtemperature of at least about 10000 p (538° C.), more typically at leastabout 12000 p (649° C.), and typically in the range of from about 1000°to about 1600° F. (from about 538° to about 871° C.). These componentsare usually exposed to turbine bleed air (e.g., air extracted from thecompressor to cool hotter components in the engine) having ingestedcorrosive components, typically metal sulfates, sulfites, chlorides,carbonates, etc., that can deposit on the surface of the component. Theceramic corrosion resistant coatings of this invention are particularlyuseful when formed on all or selected portions of the surfaces of thecomponent, such as the surfaces of turbine disks/shafts and turbine sealelements. For example, the mid-to-outer portion of the hub of a turbinedisk can have the ceramic corrosion resistant coating of this invention,while the bore region, inner portion of the hub, and blade slots mayormay not have this coating. In addition, the contact points or matingsurfaces between these components such as the disk post pressure faces(i.e., the mating surface between the disk post and the turbine bladedovetail), as well as the contact points between the disks and seals,can be void or absent of the ceramic corrosion resistant coating so asto retain desired or specified as produced dimensions.

As used herein, the term “comprising” means various coatings,compositions, metal oxides, components, layers, steps, etc., can beconjointly employed in the present invention. Accordingly, the term“comprising” encompasses the more restrictive terms “consistingessentially of” and “consisting of.”

All amounts, parts, ratios and percentages used herein are by mole %unless otherwise specified.

The various embodiments of the turbine components having the ceramiccorrosion resistant coating of this invention are further illustrated byreference to the drawings as described hereafter. Referring to FIG. 1, aturbine engine rotor component 30 is provided that can be of anyoperable type, for example, a turbine disk 32 or a turbine seal element34. FIG. 1 schematically illustrates a stage 1 turbine disk 36, a stage1 turbine blade 38 mounted to the turbine disk 36, a stage 2 turbinedisk 40, a stage 2 turbine blade 42 mounted to the turbine disk 40, aforward turbine seal 44 that also functions as a forward blade retainerfor blade 38, an aft turbine seal 46, and an interstage turbine seal 48that also functions as a forward blade retainer for blade 42, an aftblade retainer 50 for blade 38 that is held in place by seal 48, and anaft blade retainer 52 for blade 42. Any or all of these turbine disks 32(e.g., stage 1 turbine disk 36 and a stage 2 turbine disk 40), turbineseal elements 34 (e.g., forward turbine seal 44, aft turbine seal 46,and interstage turbine seal 48) and/or blade retainers 50/52, or anyselected portion thereof, can be provided with the ceramic corrosionresistant coating of this invention, depending upon whether corrosion isexpected or observed.

Referring to FIG. 2, the metal substrate 60 of the turbine engine rotorcomponent 30 can comprise any of a variety of metals, or more typicallymetal alloys, including those based on nickel, cobalt and/or ironalloys. Substrate 60 typically comprises a superalloy based on nickel,cobalt and/or iron. Such superalloys are disclosed in variousreferences, such as, for example, commonly assigned U.S. Pat. No.4,957,567 (Krueger et al), issued Sep. 18, 1990, and U.S. Pat. No.6,521,175 (Mourer et al), issued Feb. 18, 2003, the relevant portions ofwhich are incorporated by reference. Superalloys are also generallydescribed in Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed.,Vol. 12, pp. 417-479 (1980), and Vol. 15, pp. 787-800 (1981).Illustrative nickel-based superalloys are designated by the trade namesInconel®, Nimonic®, Rene® (e.g., Rene® 88, Rene® 104, Rene N5 alloys),and Udime®.

Substrate 60 more typically comprises a nickel-based alloy, andparticularly a nickel-based superalloy, that has more nickel than anyother element. The nickel-based superalloy can be strengthened by theprecipitation of gamma prime or a related phase. A nickel-basedsuperalloy for which the ceramic corrosion resistant coating of thisinvention is particularly useful is available by the trade name Rene 88,which has a nominal composition, by weight of 13% cobalt, 16% chromium,4% molybdenum, 3.7% titanium, 2.1% aluminum, 4% tungsten, 0.70% niobium,0.015% boron, 0.03% zirconium, and 0.03 percent carbon, with the balancenickel and minor impurities.

In forming the ceramic corrosion resistant coating 64 of this inventionon the surface 62 of metal substrate 60, surface 62 is typicallypretreated mechanically, chemically or both to make the surface morereceptive for coating 64. Suitable pretreatment methods include gritblasting, with or without masking of surfaces that are not to besubjected to grit blasting (see U.S. Pat. No. 5,723,078 to Niagara etal, issued Mar. 3, 1998, especially col. 4, lines 46-66, which isincorporated by reference), micromachining, laser etching (see U.S. Pat.No. 5,723,078 to Nagaraj et al, issued Mar. 3, 1998, especially col. 4,line 67 to col. 5, line 3 and 14-17, which is incorporated byreference), treatment with chemical etchants such as those containinghydrochloric acid, hydrofluoric acid, nitric acid, ammonium bifluoridesand mixtures thereof (see, for example, U.S. Pat. No. 5,723,078 toNagaraj et al, issued Mar. 3, 1998, especially col. 5, lines 3-10; U.S.Pat. No. 4,563,239 to Adinolfi et al, issued Jan. 7, 1986, especiallycol. 2, line 67 to col. 3, line 7; U.S. Pat. No. 4,353,780 to Fishter etal, issued Oct. 12, 1982, especially col. 1, lines 50-58; and U.S. Pat.No. 4,411,730 to Fishter et al, issued Oct. 25, 1983, especially col. 2,lines 40-51, all of which are incorporated by reference), treatment withwater under pressure (i.e., water jet treatment), with or withoutloading with abrasive particles, as well as various combinations ofthese methods. Typically, the surface 62 of metal substrate 60 ispretreated by grit blasting where surface 62 is subjected to theabrasive action of silicon carbide particles, steel particles, aluminaparticles or other types of abrasive particles. These particles used ingrit blasting are typically alumina particles and typically have aparticle size of from about 600 to about 35 mesh (from about 25 to about500 micrometers), more typically from about 400 to about 300 mesh (fromabout 38 to about 50 micrometers).

An embodiment of the method of this invention for forming ceramiccorrosion resistant coating 64 on metal substrate 60 is by use of asol-gel process. See commonly assigned U.S. Patent Application No.2004/0081767 (Pfaendtner et al), published Apr. 29, 2004, which isincorporated by reference. Sol-gel processing is a chemical solutionmethod to produce a ceramic oxide (e.g., zirconia). A chemicalgel-forming solution which typically comprises an alkoxide precursor ora metal salt is combined with ceramic metal oxide precursor materials,as well as any stabilizer metal oxide precursor materials, etc. A gel isformed as the gel-forming solution is heated to slightly dry it at afirst preselected temperature for a first preselected time. The gel isthen applied over the surface 62 of metal substrate 60. Properapplication of the ceramic metal oxide precursor materials and properdrying produce a continuous film over the surface 62. The sol-gel can beapplied to surface 62 of substrate 60 by any convenient technique. Forexample, the sol-gel can be applied by spraying at least one thin layer,e.g., a single thin layer, or more typically a plurality of thin layersto build up a film to the desired thickness for coating 64. The gel isthen fired at a second elevated preselected temperature above the firstelevated temperature for a second preselected time to form coating 64.The ceramic corrosion resistant coating 64 comprises a dense matrix thathas a thickness of up to about 5 mils (127 microns) and typically fromabout 0.01 to about 1 mils (from about 0.2 to about 25 microns), moretypically from about 0.04 to about 0.5 mils (from about 1 to about 13microns). Optionally, inert oxide filler particles can be added to thesol-gel solution to enable a greater per-layer thickness to be appliedto the substrate.

An alternative method for forming ceramic corrosion resistant coating 64is by physical vapor deposition (PVD), such as electron beam PVD(EB-PVD), filtered arc deposition, or by sputtering. Suitable sputteringtechniques for use herein include but are not limited to direct currentdiode sputtering, radio frequency sputtering, ion beam sputtering,reactive sputtering, magnetron sputtering and steered arc sputtering.PVD techniques can form ceramic corrosion resistant coatings 64 havingstrain resistant or tolerant microstructures such as verticalmicrocracked structures. EB-PVD techniques can form columnar structuresthat are highly strain resistant to further increase the coatingadherence. Although these strain resistant or tolerant structures havedirect paths between the coating surface 66 and the substrate 60, thepaths are sufficiently narrow that the partially molten or highlyviscous corrodant salts do not infiltrate or minimally infiltrate thecracks of the vertically microcracked structures or column gaps of thecolumnar structures.

Other suitable alternative methods for forming these ceramic corrosionresistant coating include thermal spray, aerosol spray, chemical vapordeposition (CVD) and pack cementation. As used herein, the term “thermalspray” refers to any method for spraying, applying or otherwisedepositing the ceramic composition that involves heating and typicallyat least partial or complete thermal melting of the overlay coatingmaterial and depositing of the heated/melted material, typically byentrainment in a heated gas stream, onto the metal substrate to becoated. Suitable thermal spray deposition techniques include plasmaspray, such as air plasma spray (APS) and vacuum plasma spray (YPS),high velocity oxy-fuel (HYOF) spray, detonation spray, wire spray, etc.,as well as combinations of these techniques. A particularly suitablethermal spray deposition technique for use herein is plasma spray.Suitable plasma spray techniques are well known to those skilled in theart. See, for example, Kirk-Othmer Encyclopedia of Chemical Technology,3rd Ed., Vol. 15, page 255, and references noted therein, as well asU.S. Pat. No. 5,332,598 (Kawasaki et al), issued Jul. 26, 1994; U.S.Pat. No. 5,047,612 (Savkar et al) issued Sep. 10, 1991; and U.S. Pat.No. 4,741,286 (Hoh et al), issued May 3, 1998 (herein incorporated byreference) which are instructive in regard to various aspects of plasmaspraying suitable for use herein.

Suitable methods for carrying out chemical vapor deposition and/or packcementation are disclosed in, for example, commonly assigned U.S. Pat.No. 3,540,878 (Levine et al), issued Nov. 17, 1970; commonly assignedU.S. Pat. No. 3,598,638 (Levine), issued Aug. 10, 1971; commonlyassigned U.S. Pat. No. 3,667,985 (Levine et al), issued Jun. 6, 1972,the relevant disclosures of which are incorporated by reference.Metal-organic chemical vapor phase deposition (MOCYD) processes can alsobe used herein. See commonly assigned U.S. Patent Application No.2004/0013802 (Ackerman et al), published Jan. 22, 2004, the relevantdisclosures of which are incorporated by reference.

As illustrated in FIG. 3, typically only a portion of the surface ofthese turbine disks/shafts, seals and/or blade retainers are providedwith the ceramic corrosion resistant coating 64 of this invention. FIG.3 shows a turbine disk 32 having an inner generally circular hub portionindicated as 74 and an outer generally circular perimeter or diameterindicated as 78, and a periphery indicated as 82 that is provided with aplurality of circumferentially spaced slots indicated as 86 forreceiving the root portion of turbine blades such as 38, 42. While theceramic corrosion resistant coating 64 can be applied to the entiresurface of disk 70, it is typically needed only on the surface of outerdiameter 78.

While the above embodiments have been described in the context ofcoating turbine engine disks, this invention can be used to form aceramic corrosion resistant coating 64, as described above, on thesurfaces of various turbine engine rotor components, includingcompressor disks, seals, and shafts, which can then be exposed tocorrosive elements at elevated temperatures. The ceramic corrosionresistant coatings of this invention can also be applied during originalmanufacture of the component (i.e., an OEM component), after thecomponent has been in operation for a period of time, after othercoatings have been removed from the component (e.g., a repairsituation), while the component is assembled or after the component isdisassembled, etc.

The following example illustrates an embodiment for forming the ceramiccorrosion coating of this invention on a metal substrate by sol-gelprocessing and the benefits obtained thereby:

A one inch round sample of Rene N5 alloy is coated with an approximately5 micron layer of a 7 wt. % yttria stabilized zirconia deposited from asol gel. A sulfate containing corrodant is applied to the surface of thecoating and run through a 2 hour cycle at 1300° F. (704° C.). The firsthour of the 2 hour cycle uses a reducing atmosphere to try to cause areaction between the corrodant and the surface of the coated sample,while the second hour uses air to cause corrosion scale growth. Thecorrodant is removed by water washing and coated sample is theninspected for damage. This corrosion application, thermal exposure,cleaning and inspection cycle is repeated until the coated sample showssigns of damage. After 8 cycles no appreciable damage is noted on thecoated sample. After 10 cycles, the coating is still adherent to the aHoy, but discoloration is noted and the coated sample is cross-sectionedfor evaluation. After cross-sectioning, a corrosion production layerapproximately 10 microns thick is found below the coating. Forcomparison, this is representative of a bare alloy sample (i.e., with nocoating) after approximately 2 cycles of such testing.

While specific embodiments of this invention have been described, itwill be apparent to those skilled in the art that various modificationsthereto can be made without departing from the spirit and scope of thisinvention as defined in the appended claims.

1. A method comprising the following steps: (a) providing a turbinecomponent comprising a metal substrate; and (b) depositing a ceramiccomposition comprising a ceramic metal oxide on the metal substrate byphysical vapor deposition to form a ceramic corrosion resistant coatingcomprising the ceramic metal oxide and having a strain-tolerant columnarstructure, wherein the ceramic metal oxide is selected from the groupconsisting of zirconia, hafnia and mixtures thereof.
 2. The method ofclaim 1 wherein step (b) is carried out by electron beam physical vapordeposition of the ceramic composition on the metal substrate.
 3. Themethod of claim 1 wherein the turbine component provided during step (a)is a compressor or turbine disk.
 4. The method of claim 1 wherein theturbine component provided during step (a) is a seal element.
 5. Amethod comprising the following steps: (a) providing a turbine componentother than a turbine airfoil comprising a metal substrate; and (b)thermal spraying a ceramic composition comprising a ceramic metal oxideon the metal substrate to form a ceramic corrosion resistant coatingcomprising the ceramic metal oxide, wherein the ceramic metal oxide isselected from the group consisting of zirconia, hafnia and mixturesthereof.
 6. The method of claim 5 wherein step (b) is carried out byplasma spraying the ceramic composition on the metal substrate.
 7. Themethod of claim 5 wherein the turbine component provided during step (a)is a compressor or turbine disk.
 8. The method of claim 5 wherein theturbine component provided during step (a) is a seal element.